There are five stages of sleep. Stages 1-4 are non-REM (rapid eye movement) sleep the last stage is REM sleep.
Stage 1 is when light sleep takes place, you drift in and out of sleep and noises and lights can wake you up very easily. In this stage, the eyes move slowly and muscle activity starts to slow down. In a light sleep many people experience sudden muscle twitches and can get a sensation of falling.
Stage 2, eyes stop moving and brain waves slow down, there can occasionally be a burst of rapid brain waves though. The body begins to prepare for deep proper sleep. Our body temperature begins to drop and our heart rate begins to slow down.
Stage 3, extremely slow brain waves are interspersed with smaller, faster waves. This is now deep sleep. In stage 3 people can experience sleepwalking, night terrors, talking during one’s sleep, and bedwetting. These behaviors tend to occur during the transitions between non-REM and REM sleep.
Stage 4, deep sleep continues. If you are woken up during this stage you can feel disoriented and confused for a short time.
Stage 5 REM sleep. During REM sleep our brain waves copy activity during the waking state. The eyes remain closed but move rapidly from side-to-side, this is possibly due to an intense dream and brain activity that occurs during this stage.